The synthesis of reversible oxygen-binding iron chelates will be pursued. These are modifications of the porphyrin molecule utilizing a "strapped" or "capped" structure to protect the iron from irreversible oxidation. Functional groups in the molecule will allow attachment of larger groups which will increase molecular size and, thus, lengthen circulation dwell time. The effectiveness of these chelates in transporting oxygen in vivo and in vitro will be determined. The metabolic fate of the iron and the rest of the molecule will also be established. In addition to the synthetic chelates modified hemoglobins will be prepared and biologically tested. These modifications will involve the coupling of the hemoglobin (Hb) with compounds such as high molecular weight polymers and hydroxyethyl starch (HES). The linkages between the Hb and HES or other molecules will be varied. Different ratios of Hb to HES will be used to prepare a variety of complexes having widely differing oncotic properties. The usefulness of these complexes in blood replacement in vivo and for organ perfusion in vitro will be investigated. Their metabolic fate will also be ascertained.